1. Field of the Invention
The present invention relates generally to assistive medical devices. More particularly, the present invention relates to a device for assisting and augmenting the movements of a person with neuromuscular abnormalities or weakness.
2. Background Description
Individuals with neuromuscular abnormalities, such as anterior horn cell disease or muscular disorders (e.g., Muscular Dystrophy), often lose the ability to place their limbs in space due to the weakening of their proximal muscles. Typically, the muscles of these individuals become so weak that they cannot support their arms against gravity, thereby making it difficult to perform routine tasks such as eating.
An orthosis is an exoskeletal device that is attached to flail or weakened limbs to augment strength deficiency. Articulated upper limb orthoses, ranging from the mobile arm support to electrically powered wrist-hand orthoses, have been investigated for a number of years.
Among the earliest and most accepted devices is the Balanced Forearm Orthosis (xe2x80x9cBFOxe2x80x9d), also called the mobile arm support. The BFO, a passive (e.g., body-powered) device was developed in 1965, and provides people with weak musculature the ability to move their arms in a horizontal plane. Two linkages having joints along the vertical axes accomplish this task. One end of the BFO is attached to a wheelchair, while the other end is connected to a trough into which a person places his or her forearm. The trough uses a fulcrum at mid-forearm that permits the hand to elevate if the shoulder is depressed. The BFO allows a person to move horizontally, for example, over a lap tray, and to use compensatory movements to attain limited movement in the vertical direction.
An enhanced version of the BFO allows vertical movement by providing a horizontal joint at the base. Attaching rubber bands to the joint compensates for the weight of the arm. Due to the inexact gravity compensation that results, this device is rarely prescribed. The majority of BFO users settle for planar movement and rely on compensatory body movements to achieve vertical motions.
Various forms of overhead slings that allow for movement in three dimensions have also been used to assist arms with proximal weakness. These devices, in addition to being aesthetically unappealing, are prone to oscillations when the arm is moved. One such overhead device is the Musgrave orthosis, which uses a weight at the back of a wheelchair to counterbalance the arm.
The first computerized orthosis was developed at the Case Institute of Technology in the early 1960s. The manipulator was configured as a floor mounted, four degree-of-freedom, externally powered exoskeleton. Control of this manipulator was achieved using a head-mounted light source to trigger light sensors in the environment.
Rancho Los Amigos Hospital continued the Case orthosis and developed a six degree-of-freedom, electrically driven xe2x80x9cGolden Arm.xe2x80x9d The Rancho xe2x80x9cGolden Armxe2x80x9d had a configuration similar to the Case arm, but was without computer control. It was significant, however, in that it was mounted on a wheelchair and was found to be useful by people who had disabilities with intact sensation resulting from polio or multiple sclerosis. The Rancho xe2x80x9cGolden Armxe2x80x9d was controlled at the joint level by seven tongue-operated switches, which made operation very tedious. The xe2x80x9cGolden Armxe2x80x9d was subsequently modified to add computer control and input from eye trackers.
In 1975, the Burke Rehabilitation Center modified the BFO by adding actuators. Direct current motors powered the Burke orthosis, with five degrees-of-freedom, including pronation/supination and elbow flexion/extension. However, control was maintained through use of a joystick, control pad, or various microswitch assemblies, making it a less-than-ideal interface.
Examples of other orthoses that have not gone beyond the prototype stage include the hybrid arm orthosis, which was externally powered and controlled by a combination of contralateral shoulder movement and air switches operated by the head, and the powered orthotic device for the enhancement of upper limb movement. This latter project was conducted at The Hugh Macmillan Rehabilitation Center and targeted people with amyotrophic lateral sclerosis. This mechanism allowed three degrees-of-freedom, used external power, and was controlled by signals from the eyebrows.
While the existing orthosis devices have advanced the state of the knowledge in design of orthoses that interact with humans with disabilities, the technology has yet to make a significant impact on the lives of people with disabilities. This is in large part due to the complex control requirements of the devices and the prohibitive cost of powered devices.
It is an object of the present invention to provide an orthosis device with a natural human-machine interface.
Another object of the present invention is to provide a fully functional yet cost-efficient orthosis device.
Yet another object of the present invention is to provide a gravity-balanced sense of xe2x80x9cfloatationxe2x80x9d that will allow a person with neuromuscular weakness to move his or her limbs with minimal effort.
Still another object of the present invention is to provide an orthosis device adaptable to a range of user weights and disabilities.
The present invention is an orthosis device for providing a gravity-balanced equilibrium for a limb of a user. The orthosis device generally includes two limb sections that are pivotably connected in at least one, and preferably two, degrees of freedom. Each of the two limb sections comprises a four-bar linkage and a spring member adapted to provide an equilibrium-inducing force corresponding to a combined weight of the limb section and the user""s limb attached thereto. The equilibrium-inducing force allows every position in three-dimensional space to be a balanced position, such that minimal effort is required to move the limb or hold it in place.
Two mounting mechanisms attached to each limb section are used to attach the spring member. At least one of the mounting mechanisms may be adjustable to pre-stress the spring member, allowing a single embodiment of the orthosis device to be used for individuals of a range of weights. Furthermore, individuals with varying degrees of muscular degeneration can be accommodated by including force sensors and power actuators.
The orthosis device, in embodiments, includes a shoulder bracket for mounting the orthosis device on a wheelchair. The shoulder bracket includes several pivotably connected links, which adds additional degrees of freedom to the orthosis device. Thus, the orthosis device according to the present invention allows for anatomical movement in essentially four degrees of freedom: two at the elbow and two at the shoulder.